The invention relates to a moulded piece forming a negative mould of at least a part of a chute of a shaft bottom which moulded piece is formed from a material forming a dead core and, optionally being assembled with at least one further moulded piece, forms the negative mould of a chute of a shaft bottom in the form of a moulded body, wherein the moulded piece(s) is (are) designed for being placed onto a mould bottom of a bottom mould for a shaft bottom and has (have) a linear and/or an arcuate longitudinal extension, as well as to a mounting appliance for the production of the moulded piece.
Shaft bottoms form the lower impervious closure of normally vertical shafts which permit sewage systems to have access to canals such as sewers and underground pipeline systems. Such shafts are often located at intersecting points of canals or pipeline systems, respectively, i.e. at canal branchings or outlets and inlets, respectively, of subsidiary canals etc. The shaft bottoms forming the lower closure of such shafts are pot-shaped formations having a comparatively thick-walled impervious bottom and a mostly cylindrical side wall in which connection ports for the pipes and/or canals are formed. Canals open at the top and usually having a semicircular or roughly U-shaped cross-section, which are referred to as chutes, run in the shaft bottom between the respective connection ports provided in the side wall of a shaft bottom. In order to guarantee a congestion-free flow of the fluids which often are contaminated by substantial amounts of lumpy solids, the chutes have a certain gradient and the shaft bottom has a tread with a small inclination, also referred to as a berm.
Although the shafts are composed of standardized individual rings, the shaft bottoms are uniquely shaped components which differ in terms of the positioning of the connection ports functioning as inflows and outflows, the cross-sectional shape of the chutes and the pipes to be connected thereto. Moreover, only high-quality fluid-tight concrete may be used for the manufacture of lower shaft parts and in particular of the chutes thereof.
From DE 36 11 394 A1 it is known for the production of a shaft bottom to arrange a mould bottom, the top side of which is shaped according to the negative mould of the chute, in a bottom mould which has a mantle placed on a base plate. Such a mould bottom is usable again and again—after sufficient hardening of the concrete, it is removed from the mantle, is cleaned and can then be available for reuse. A disadvantage is the very complicated manufacture of such a mould bottom; for the production of uniquely shaped shaft bottoms, the same number of costly mould bottoms would have to be provided, i.e. a separate mould bottom would have to be provided for almost every shaft bottom. Since this is far too expensive, the device known from this document is used only for a small number of shaft bottoms, for instance, if a chute crosses the shaft bottom in a straight line or bent by 90° for example.
For shaft bottoms the chutes of which are to be connected to two canals running in different directions or which exhibit other special features, for cost reasons, shaft bottoms with a level bottom have been produced and the chute is manufactured on the level bottom by introducing concrete manually and forming the chute by hand. This kind of manual labour is tedious, since it is necessary to bend forward into the shaft bottom over the side wall thereof. Furthermore, the chute has to be formed with great accuracy so that both the gradient and the position of the secondary arms of the canal correspond to the local conditions of the canal system or of the pipeline system, respectively. This manual production of a chute requires qualified personnel and, for that reason, is expensive. Moreover, it also involves a substantial expenditure of time, and furthermore the quality of the manually formed concrete is not comparable with the quality of a shaft bottom that has been produced mechanically.
From DE 43 42 518 A1, it is known to form the chute by inserting a clay shell element which remains in the shaft bottom after the completion thereof, forming the bottom of the chute. Also in this case it is difficult to produce chutes to be designed individually, particularly since a separate clay shell element would have to be prefabricated for each chute, which likewise involves high expenses.
According to a further suggestion concerning the manufacture of a shaft bottom, prefabricated moulded plastic parts are used with a negative mould corresponding to the chute, whereby a separate moulded part has to be manufactured for each individual chute, which moulded part is to be fixed to the mould bottom. Said moulded parts are produced as plastic shells for each individual chute according to the respective course of the chute, involving relatively high expenses, and remain as so-called dead moulds in the finished chute. A disadvantage of this process, besides the high costs for the moulded parts designed as high-quality plastic shells, is the manufacture necessarily taking place at external suppliers, whereby the entire logistics for the mechanical production of lower shaft parts becomes rather more complicated.
It is internally known (Austrian patent application A 653/2003) for the production of a shaft bottom to provide moulded pieces for the formation of a moulded body, which moulded pieces are manufactured from a material withstanding the pressure of the concrete such as from a foamed material, in particular a rigid-foamed synthetic material or a thermoplastic synthetic material such as EPS, respectively. Said moulded pieces suitably have a linear or an arcuate longitudinal extension, with the cross-section corresponding to the cross-section of the chute and with the height of the cross-section of the moulded pieces optionally being dimensioned larger than the height of the cross-section of the chute.
Such prefabricated moulded pieces ensure the mechanical production of shaft bottoms comprising chutes of predetermined cross-sections without elaborate moulding. It is merely necessary to provide for a seamless transition between the individual moulded pieces. For this purpose, possible gaps between the moulded pieces or between the moulded pieces and the mould bottom, respectively, or around the clearance pieces, respectively, can be covered and/or filled up by a joint filler.
Due to the thermoplastic properties of the foamed materials that are used, the profiled pieces can be trimmed arbitrarily not only on the face side but also in the area of the attachment surface facing the tread surface of the mould bottom by means of a resistance wire in a comparatively simple manner. The advance of the resistance wire can be controlled mechanically depending on the shape that is required in each case.